A diamond-tipped stylus, which is used in the laboratory for marking glass slides, is the most serviceable instrument for cutting glass ampuls, as it is not dulled by use as are metallic scoring devices. Since, however, the operator's thumb must exert counterpressure against the ampul as it is rotated against the stylus, there is a constant danger of laceration of the thumb if the ampul breaks unexpectedly. To obviate this hazard, the guard shown in the accompanying figure was devised. The dimensions are approximations that will vary according to the size of the stylus. The guard can be easily cut with heavy shears from 1/32-in sheet aluminum, which can be obtained at most hardware stores. The shank is rolled to envelop the shaft of the stylus, and the hood is shaped for the convenience of the operator. It is slipped onto the stylus so that the thumb rest holds the